Infant safety seats are of course well known and have been in use for many years for the purpose of protecting youngsters travelling in cars. Typically, such seats include a rigid framework for supporting the seat portion and protecting the child, and a harness system used to strap the child securely within the seat in the event of an accident. Virtually all commercially available seats of this sort are sold as stand-alone units which are removably installed using the car's seat belt to restrain the lower portion of the seat, and a strap with a hook or similar mechanism for anchoring the top of the seat to the vehicle frame.
The problem with such seats is of course that they are intrusive and occupy seat space even when not in use to transport children. Larger persons using the back seat of the vehicle which is where infant seats are usually installed must crowd around the safety seat, or the seat must be removed to accommodate extra passengers. Removal can be an awkward and time consuming process. Obviously, when the seat is again required, it must of course be reinstalled, which can be equally awkward.